Why is texture paint mirroring?
Your normals are inverted (they are going inside the model).
Texture paint paints on front normals. That's why when you think you paint the front, all is going to the back.
To see the normals (edit mode) : go to the "mesh display" part of the right panel of the 3D view.
To inverse the normals, select all the needed vertices, then ctrl+N or ctrl+shift+N.